A heart valve prosthesis includes a downstream first axial end (6) and an upstream second axial end (8) and a stitching ring (10) extending in an arcuate manner for stitching in a blood vessel. The arcuate course of the stitching ring (10) is formed by three arcs (12) and three transition regions (14). At each end of two of the arcs (12) transition into each other. The stitching ring (10) has a movable tab (18) at at least one of the three transition regions (14). The movable tab (18) can be selectively directed toward the first axial end (6) or folded over toward the second axial end (8).